Epoxy systems consist of two components that can chemically react with each other to form a cured epoxy, which is a hard, inert material. The first component is an epoxy resin and the second component is a curing agent, sometimes called a hardener. Epoxy resins are substances or mixtures that contain epoxide groups. The hardener includes compounds that are reactive with the epoxide groups of the epoxy resins.
The epoxy resins can be crosslinked, also referred to as curing, by the chemical reaction of the epoxide groups and the compounds of the hardener. This curing converts the epoxy resins, which have a relatively low molecular weight, into relatively high molecular weight materials by chemical addition of the compounds of the hardener.
Epoxy systems are used in a great variety of applications, including coatings. Coatings are used to treat surfaces to protect against corrosion and other forms of degradation caused by use and/or the environment. The types of surfaces treated include concrete, metal, and other surfaces.
Some epoxy systems used for coatings are liquid based systems. Some of the liquid based systems contain volatile organic solvents. Volatile organic solvents are becoming less desirable for some applications and use of these liquid based systems has been curtailed. Some other liquid based systems are solvent free. The solvent free liquid based systems can require costly, non-standardized equipment for application of the coating. However, the solvent free liquid based systems, like other liquid based systems, have disadvantages including premixing, monitoring and maintenance of viscosity, and the possibility of running or sagging during and after application of the coating.
Some other epoxy systems used for coatings are solid based systems. Powder coatings are examples of solid based systems. Powder coatings can be formed when a solid epoxy resin, a solid hardener, and other elements, if desired, are combined by melting and extruded. The molten extrudate can be cooled and milled to a desired particle size for the particular application. The powder coating can be applied to an article via a spray gun, by exposing the article to a fluidized bed of the powder coating, or by another procedure. Following the application of the powder coating to the article the epoxy system is cured. The article thus coated.
There are many possible uses for powder coatings, and there are a great variety of characteristics that may desirable for particular applications.